U.S. patent number 7,746,968 [Application Number 11/722,036] was granted by the patent office on 2010-06-29 for beam combining and hybrid beam selection method for improving digital broadcasting reception performance, and digital broadcasting receiving apparatus using the same.
This patent grant is currently assigned to Electronics and Telecommunications Research Institute. Invention is credited to Jae-Hwui Bae, Ju-Yeun Kim, Young-Su Kim, Hyun Lee, Soo-In Lee, Jong-Soo Lim.
United States Patent |
7,746,968 |
Kim , et al. |
June 29, 2010 |
Beam combining and hybrid beam selection method for improving
digital broadcasting reception performance, and digital
broadcasting receiving apparatus using the same
Abstract
Provided are a beam combining and hybrid beam selection method
that can improve digital broadcasting reception performance by
combining more than two beam output signals (beam combination type)
instead of simply selecting one of beam output signals (beam
selection type), or even selecting an optimal method between the
beam selection type and the beam combination type, and a digital
broadcasting receiving apparatus using the same.
Inventors: |
Kim; Ju-Yeun (Daegu,
KR), Kim; Young-Su (Daejeon, KR), Bae;
Jae-Hwui (Daejeon, KR), Lee; Hyun (Daejeon,
KR), Lim; Jong-Soo (Daejeon, KR), Lee;
Soo-In (Daejeon, KR) |
Assignee: |
Electronics and Telecommunications
Research Institute (Daejeon, KR)
|
Family
ID: |
36588038 |
Appl.
No.: |
11/722,036 |
Filed: |
July 4, 2005 |
PCT
Filed: |
July 04, 2005 |
PCT No.: |
PCT/KR2005/002117 |
371(c)(1),(2),(4) Date: |
June 18, 2007 |
PCT
Pub. No.: |
WO2006/065011 |
PCT
Pub. Date: |
June 22, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080092194 A1 |
Apr 17, 2008 |
|
Foreign Application Priority Data
|
|
|
|
|
Dec 17, 2004 [KR] |
|
|
10-2004-0108298 |
|
Current U.S.
Class: |
375/347 |
Current CPC
Class: |
H04B
7/088 (20130101); H04N 5/211 (20130101); H01Q
25/00 (20130101); H04N 21/426 (20130101); H04N
21/42638 (20130101) |
Current International
Class: |
H04B
7/10 (20060101) |
Field of
Search: |
;375/347 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1020020049358 |
|
Jun 2002 |
|
KR |
|
1020040027210 |
|
Apr 2004 |
|
KR |
|
Other References
Moon, et al.; "Spatial Diversity Technique for Improvement of DTV
Reception Performance"; IEEE Transactions on Consumer Electronics;
vol. 49, No. 4; pp. 958-964; Nov. 2003. cited by other .
Meehan; "Antenna Diversity For Improving Indoor Reception Of US
Digital Terrestrial Television Receivers"; IEEE Transactions on
Consumer Electronics; vol. 48, No. 4; pp. 850-853; Nov. 2002. cited
by other .
Kim, et al.; "ATSC Digital TV Receiver using Spatial Diversity
Technique"; IEEE 60th Vehicular Technology Conference Fall 2004;
vol. 1; pp. 310-313; Sep. 2004. cited by other .
International Search Report dated Nov. 14, 2005 for Application No.
PCT/KR2005/002117 (All references cited in Search Report are listed
above). cited by other.
|
Primary Examiner: Kim; Kevin Y
Attorney, Agent or Firm: Park; Jae Y. Kile Goekjian Reed
& McManus
Claims
What is claimed is:
1. A beam combining method in a digital broadcasting receiving
apparatus, the beam combining method comprising the steps of:
calculating SMNRs (mainpath signal to multipath signals and noise
ratios) with respect to a plurality of beam output signals, formed
according to directions from a plurality of antenna output signals
whose phases are shifted depending on arrangement positions of
array antennas, by using corresponding channel impulse responses;
selecting a predetermined number of beam output signals according
to values of the SMNRs by comparing the calculated SMNRs with
respect to the respective beam output signals; calculating a delay
time between mainpath signals of the selected beam output signals;
and generating a combined beam output signal by combining the two
beam output signals by adjusting the calculated delay time.
2. The beam combining method as recited in claim 1, wherein the
SMNRs are calculated under conditions that a signal having the
greatest amplitude is considered as a mainpath signal and the
remaining signals are considered as multipath signals and
noises.
3. The beam combining method as recited in claim 2, wherein the two
beam output signals are combined using an equal gain combining
(EGC) method or a maximal ratio combining (MRC) method, and the
delay time is compensated and added thereto.
4. A beam selecting method in a digital broadcasting receiving
apparatus, the beam selecting method comprising the steps of: a)
calculating SMNRs (mainpath signal to multipath signal and noise
ratios) with respect to a plurality of beam output signals, formed
according to directions from a plurality of antenna output signals
whose phases are shifted depending on arrangement positions of
array antennas, by using corresponding channel impulse responses;
b) selecting a first predetermined number of beam output signals
according to values of the SMNRs by comparing the calculated SMNRs
with respect to the respective beam output signals; c) calculating
a delay time between mainpath signals of the selected beam output
signals, and generating a combined beam output signal by combining
the two beam output signals by adjusting the calculated delay time;
d) when the SMNR of the combined beam output signal is less than
the maximal SMNR of the selected beam output signals, calculating
an SDMR (mainpath signal to dominant multipath signal ratio) with
respect to the respective beam output signals, and selecting a beam
output signal having the greatest SDMR; and e) calculating an SMNR
of the combined beam output signal using channel impulse response
of the combined beam output signal, and comparing the calculated
SMNR with a maximal value among the SMNRs of the selected beam
output signals; and f) when the SMNR of the combined beam output
signal is greater than or equal to the maximal SMNR of the selected
output signals, selecting the combined beam output signal generated
in step c).
5. The beam selecting method as recited in claim 4, wherein the
step e) includes the steps of: e1) selecting a predetermined number
of beam output signals according to magnitudes of the SMNRs by
comparing the calculated SMNRs with respect to the respective beam
output signals; e2) calculating SDMRs with respect to the beam
output signals selected in the step e1) by using corresponding
channel impulse responses; and e3) comparing the SDMRs calculated
in the step e2) and selecting a beam output signal having the
greatest SDMR.
6. The beam selecting method as recited in claim 5, wherein the
SMNRs are calculated under conditions that a signal having the
greatest amplitude is considered as a mainpath signal and the
remaining signals are considered as multipath signals and
noises.
7. The beam selecting method as recited in claim 6, wherein the two
beam output signals are combined using an equal gain combining
(EGC) method or a maximal ratio combining (MRC) method, and the
delay time is compensated and added thereto.
8. A digital broadcasting receiving apparatus using beam
combination, comprising: a plurality of RF front ends for
converting RF signals, received through antenna elements of array
antennas, into digital signals of IF band; a plurality of
beamformers for forming different beams depending on directions by
using the IF signals outputted from the RF front ends; a plurality
of demodulators for demodulating the beam output signals of the
beamformer into baseband signals of symbol unit; a plurality of
correlators for generating channel impulse responses by correlating
the output signals of the demodulators with a training sequence
signal; a beam combiner for calculating SMNRs with respect to
channel impulse responses generated from the correlators and
generating a beam combined output signal by selecting and combining
a predetermined number of beam output signals according to
magnitudes of the SMNRs; and an equalizer for compensating for
channel distortion in the output signal of the beam combiner.
9. The digital broadcasting receiving apparatus as recited in claim
8, wherein the beam combiner performs a function of calculating
SMNRs (mainpath signal to multipath signal and noise ratios) with
respect to a plurality of beam output signals, formed according to
directions from a plurality of antenna output signals whose phases
are shifted depending on arrangement positions of array antennas,
by using corresponding channel impulse responses; a function of
selecting a predetermined number of beam output signals according
to magnitudes of the SMNRs by comparing the calculated SMNRs with
respect to the respective beam output signals; a function of
calculating a delay time between mainpath signals of the selected
beam output signals; and a function of generating a combined beam
output signal by combining the two beam output signals by using the
calculated delay time.
10. The digital broadcasting receiving apparatus as recited in
claim 9, wherein the SMNRs are calculated under conditions that a
signal having the greatest amplitude is considered as a mainpath
signal and the remaining signals are considered as multipath
signals and noises.
11. The digital broadcasting receiving apparatus as recited in
claim 10, wherein the two beam output signals are combined using an
equal gain combining (EGC) method or a maximal ratio combining
(MRC) method, and the delay time is compensated and added
thereto.
12. A digital broadcasting receiving apparatus using hybrid beam
selection, comprising: a plurality of RF front ends for converting
RF signals, received through antenna elements of array antennas,
into digital signals of IF band; a plurality of beamformers for
forming different beams depending on directions by using the IF
signals outputted from the RF front ends; a plurality of
demodulators for demodulating the beam output signals of the
beamformer into baseband signals of symbol unit; a plurality of
correlators for generating channel impulse responses by correlating
the output signals of the demodulators with a training sequence
signal; a hybrid beam selector for calculating first SMNR with
respect to the respective channel impulse responses, generating a
beam combined output signal by selecting and combining a
predetermined number of beam output signals according to magnitudes
of the first SMNRs, and performing one of a beam selecting method
and a beam combining method by comparing a second SMNR calculated
using a channel impulse response of the beam combined output signal
with a maximal value of the first SMNRs; and an equalizer for
compensating for channel distortion in the output signal of the
beam combiner.
13. The digital broadcasting receiving apparatus as recited in
claim 12, wherein the hybrid beam selector performs a function a)
of calculating SMNRs (mainpath signal to multipath signal and noise
ratios) with respect to a plurality of beam output signals, formed
according to directions from a plurality of antenna output signals
whose phases are shifted depending on arrangement positions of
array antennas, by using corresponding channel impulse responses; a
function b) of selecting a first predetermined number of beam
output signals according to magnitudes of the SMNRs by comparing
the calculated SMNRs with respect to the respective beam output
signals; a function c) of calculating a delay time between mainpath
signals of the selected beam output signals, and generating a
combined beam output signal by combining the two beam output
signals by using the calculated delay time; a function d) of
calculating an SDMR (mainpath signal to dominant multipath signal
ratio) with respect to the respective beam output signals when the
SMNR of the combined beam output signal is less than the maximal
SMNR of the selected beam output signals, and selecting a beam
output signal having the greatest SDMR; and a function e) of
calculating an SMNR of the combined beam output signal using
channel impulse response of the combined beam output signal, and
comparing the calculated SMNR with a maximal value among the SMNRs
of the selected beam output signals; and a function f) of selecting
the combined beam output signal generated in the function c) when
the SMNR of the combined beam output signal is greater than or
equal to the maximal SMNR of the selected output signals.
14. The digital broadcasting receiving apparatus as recited in
claim 13, wherein the function e) includes the functions of: e1)
selecting a predetermined number of beam output signals according
to magnitudes of the SMNRs by comparing the calculated SMNRs with
respect to the respective beam output signals; e2) calculating
SDMRs with respect to the beam output signals selected in the
function e1) by using corresponding channel impulse responses; and
e3) comparing the SDMRs calculated in the function e2) and
selecting a beam output signal having the greatest SDMR.
15. The digital broadcasting receiving apparatus as recited in
claim 14, wherein the SMNRs are calculated under conditions that a
signal having the greatest amplitude is considered as a mainpath
signal and the remaining signals are considered as multipath
signals and noises.
16. The digital broadcasting receiving apparatus as recited in
claim 15, wherein the two beam output signals are combined using an
equal gain combining (EGC) method or a maximal ratio combining
(MRC) method, and the delay time is compensated and added thereto.
Description
TECHNICAL FIELD
The present invention relates to a beam combining and hybrid beam
selection method for improving digital broadcasting reception
performance, and a digital broadcasting receiving apparatus using
the same; and, more particularly, to a beam combining and hybrid
beam selection method for improving digital broadcasting reception
performance, and a digital broadcasting receiving apparatus using
the same, in which more than two beam output signals instead of
selecting one of beam output signals are combined (beam combination
type), or an optimal method of a beam selection type or a beam
combination type is selected.
BACKGROUND ART
Advanced Television Systems Committee (ATSC) digital TV (DTV)
transmission scheme can transmit high quality of image at a high
data rate, but is greatly dependent on multipath signals with large
amplitude or characteristics of Doppler shift. Therefore, in poor
channel environments, such as indoor reception environment or
mobile reception environment, an equalizer of a DTV receiver does
not completely compensate for channel distortion, thus greatly
degrading reception performance. To solve this limitation, channel
distortion that must be compensated by the equalizer is reduced by
performing signal processing in spatial domain as well as time
domain.
Conventional beamforming techniques that can achieve a spatial
signal processing are classified into an adaptive beamforming
signal processing and a selective beamforming signal
processing.
The adaptive beamforming method calculates beamforming weight
coefficients in real time and adaptively. On the contrary, the
selective beamforming method forms several beams using weight
coefficients fixed in a designated direction and selects a signal
having the highest reception performance among several beam
outputs. Consequently, the selective beamforming method can be
implemented more easily than the adaptive beamforming method and
has a high applicability to the DTV system.
That is, the selective beamforming method draws attraction because
it can improve the reception performance in a relatively simple way
by the combination with the DTV receiver. Regarding a received
signal passing through the selective beamforming system, multipath
signals are somewhat removed and then inputted to the DTV receiver.
Therefore, the equalizer of the DTV receiver can compensate for the
distorted channels in a relatively simple way.
However, since the conventional selective beamforming method also
selects only one of several beam output signals, there exists the
limitation in improving the reception performance. Therefore, there
is a demand for calculating beams with channel characteristic
improved much more than the selective beamforming method by
selecting more than two beams satisfying a criteria condition of
channel characteristic, instead of selecting only one beam output
signal, and combining selected beam output signals.
DISCLOSURE
Technical Problem
It is, therefore, an object of the present invention to provide a
beam combining and hybrid beam selection method that can improve
digital broadcasting reception performance by combining more than
two beam output signals (beam combination type) instead of simply
selecting one of beam output signals (beam selection type), or even
selecting an optimal method between the beam selection type and the
beam combination type, and a digital broadcasting receiving
apparatus using the same.
Other objects and advantages of the present invention can be
understood more fully through the embodiments of the present
invention. Also, the objects and advantages of the present
invention can be easily implemented by means of the following
claims and combination thereof.
Technical Solution
In accordance with one aspect of the present invention, there is
provided a beam combining method in a digital broadcasting
receiving apparatus, the beam combining method including the steps
of: calculating SMNRs (mainpath signal to multipath signals and
noise ratios) with respect to a plurality of beam output signals,
formed according to directions from a plurality of antenna output
signals whose phases are shifted depending on arrangement positions
of array antennas, by using corresponding channel impulse
responses; selecting a predetermined number of beam output signals
according to values of the SMNRs by comparing the calculated SMNRs
with respect to the respective beam output signals; calculating a
delay time between mainpath signals of the selected beam output
signals; and generating a combined beam output signal by combining
the two beam output signals by adjusting the calculated delay
time.
In accordance with another aspect of the present invention, there
is provided a beam selecting method in a digital broadcasting
receiving apparatus, the beam selecting method including the steps
of: a) calculating SMNRs (mainpath signal to multipath signals and
noise ratios) with respect to a plurality of beam output signals,
formed according to directions from a plurality of antenna output
signals whose phases are shifted depending on arrangement positions
of array antennas, by using corresponding channel impulse
responses; b) selecting a first predetermined number of beam output
signals according to magnitudes of the SMNRs by comparing the
calculated SMNRs with respect to the respective beam output
signals; c) calculating a delay time between mainpath signals of
the selected beam output signals, and generating a combined beam
output signal by combining the two beam output signals by adjusting
the calculated delay time; d) when the SMNR of the combined beam
output signal is less than the maximal SMNR of the selected beam
output signals, calculating an SDMR (mainpath signal to dominant
multipath signal ratio) with respect to the respective beam output
signals, and selecting a beam output signal having the greatest
SDMR; and e) calculating an SMNR of the combined beam output signal
using channel impulse response of the combined beam output signal,
and comparing the calculated SMNR with a maximal value among the
SMNRs of the selected beam output signals; and f) when the SMNR of
the combined beam output signal is greater than or equal to the
maximal SMNR of the selected output signals, selecting the combined
beam output signal generated in step c).
In accordance with a further aspect of the present invention, there
is provided a digital broadcasting receiving apparatus using beam
combination, including: a plurality of RF front ends for converting
RF signals, received through antenna elements of array antennas,
into digital signals of IF band; a plurality of beamformers for
forming different beams depending on directions by using the IF
signals outputted from the RF front ends; a plurality of
demodulators for demodulating the beam output signals of the
beamformer into baseband signals of symbol unit; a plurality of
correlators for generating channel impulse responses by correlating
the output signals of the demodulators with a training sequence
signal; a beam combiner for calculating SMNRs with respect to
channel impulse responses generated from the correlators and
generating a beam combined output signal by selecting and combining
a predetermined number of beam output signals according to values
of the SMNRs; and an equalizer for compensating for channel
distortion in the output signal of the beam combiner.
In accordance with a still further another embodiment of the
present invention, there is provided a digital broadcasting
receiving apparatus using hybrid beam selection, including: a
plurality of RF front ends for converting RF signals, received
through antenna elements of array antennas, into digital signals of
IF band; a plurality of beamformers for forming different beams
depending on directions by using the IF signals outputted from the
RF front ends; a plurality of demodulators for demodulating the
beam output signals of the beamformer into baseband signals of
symbol unit; a plurality of correlators for generating channel
impulse responses by correlating the output signals of the
demodulators with a training sequence signal; a hybrid beam
selector for calculating first SMNR with respect to the respective
channel impulse responses, generating a beam combined output signal
by selecting and combining a predetermined number of beam output
signals according to values of the first SMNRs, and performing one
of a beam selecting method and a beam combining method by comparing
a second SMNR calculated using a channel impulse response of the
beam combined output signal with a maximal value of the first
SMNRs; and an equalizer for compensating for channel distortion in
the output signal of the beam combiner.
Advantageous Effects
In accordance with the present invention, performance of a DTV
receiver can be improved in mobile reception and indoor reception
environment by providing a beam combining method using a reliable
beam selection.
Also, a beam combining method in accordance with the present
invention can increase an equalization speed of a receiver and an
output SNR by compensating for time delay alone without special
signal processing with respect to beam outputs to be combined.
Further, a hybrid beam selecting method in accordance with the
present invention can remarkably improve the performance of a
receiver by selecting an optimal one of a beam selecting structure
and a beam combining structure through comparison of channel
impulse responses after beam combination, instead of selecting and
combining beams.
DESCRIPTION OF DRAWINGS
The above and other objects and features of the present invention
will become apparent from the following description of the
preferred embodiments given in conjunction with the accompanying
drawings, in which:
FIG. 1 is a block diagram of a beam combining type digital
broadcasting receiving apparatus and a hybrid beam selecting type
digital broadcasting receiving apparatus in accordance with an
embodiment of the present invention;
FIG. 2 is a flowchart of a beam selecting method in accordance with
an embodiment of the present invention;
FIGS. 3 to 7 illustrate channel impulse responses of beam outputs
according to steering angles of beams used in the beam selecting
method of FIG. 2;
FIG. 8 is a flowchart of a beam combining method for improving a
digital broadcasting reception performance in accordance with an
embodiment of the present invention;
FIGS. 9 to 13 illustrate channel impulse responses of the beam
outputs used in the beam combination of FIG. 8;
FIGS. 14 and 15 illustrates output signals of the equalizer in the
beam selection type DTV receiving apparatus and the beam
combination type DTV receiving apparatus, respectively;
FIGS. 16 and 17 illustrates mean square error of the output signals
of the equalizer in the beam selection type DTV receiving apparatus
and the beam combination type DTV receiving apparatus,
respectively;
FIGS. 18 and 19 illustrate tap coefficients of the equalizer in the
beam selection type DTV receiving apparatus and the beam
combination type DTV receiving apparatus; and
FIG. 20 is a flowchart of a hybrid beam selecting method for
improving the digital broadcasting reception performance in
accordance with an embodiment of the present invention.
BEST MODE FOR THE INVENTION
Other objects and aspects of the invention will become apparent
from the following description of the embodiments with reference to
the accompanying drawings, which is set forth hereinafter.
FIG. 1 is a block diagram of a beam combining type digital
broadcasting receiving apparatus and a hybrid beam selecting type
digital broadcasting receiving apparatus in accordance with an
embodiment of the present invention. One of a beam combiner or a
hybrid beam selector 105 is used.
When the number of array antennas 100 and the direction and number
of beam are determined, weight values based on the direction are
determined. In FIG. 1, M represents the number of array antennas
and N represents the number of the determined beam.
Signals inputted to the antenna elements are incident with
different phase shifts according to positions of the antenna array.
The signals incident onto the antennas pass through an RF front end
101 and finally produces digital signals of IF band.
N number of beamformers 101 form different beams according to the
beam directions and receive output signals of M number of RF front
ends 101. A demodulator 103 demodulates an output signal of the
beamformer 102 into baseband signal of symbol unit.
In order to estimate channel impulse response, the output signal of
the demodulator 104 passes through a correlator 104. The correlator
104 calculates the channel impulse response using a cross
correlation between the output signal of the demodulator and a
PN511 signal of a field segment. The PN511 signal of the field
segment is a kind of a training sequence.
If an incident angle of a mainpath signal inputted to the antenna
is 10.degree. and incident angles of the remaining multipath
signals are respectively -33.degree., -66.degree., 60.degree.,
35.degree. and 63.degree., channel impulse responses of five beam
outputs are exhibited like FIGS. 9 and 10. They are output signals
of the correlator 104.
If the output signals of N number of the correlators 104 are
transferred to the beam combiner or hybrid beam selector 105,
signals are combined/selected by the beam combiner or hybrid beam
selector 105 and then inputted to an equalizer 106.
The equalizer 106 compensates for channel distortion remaining in
the output signals of the beam comber or hybrid beam selector
105.
FIG. 2 is a flowchart of a beam selecting method in accordance with
an embodiment of the present invention. The flowchart of FIG. 2
represents an algorithm for reliable beam selection that can most
improve the reception performance among several beams. This method
is carried out in the beam selector 105. That is, the beam
selecting method is the beam selecting algorithm for transferring
signals having less distortion to the equalizer 106 of the DTV
receiver.
In accordance with this algorithm, characteristics of several beam
output signals are examined, instead of one beam output signal.
Then, a plurality of beam output signals are selected which have
strong possibility of channel improvement in which multipath
signals are much removed. Using these signals, channel improvement
is maximized, thus improving the performance of the DTV
receiver.
The beam selecting method is to select optimal beam using a
mainpath signal to multipath signal and noise ratio (SMNR) and a
mainpath signal to dominant multipath signal ratio (SDMR), which
will be described below in detail.
In step 201, the beam selector 105 calculates SMNRs with respect to
the respective beam output signals by using channel impulse
responses estimated by the correlator 104. Specifically, as
illustrated in FIGS. 3 to 7, the SMNRs are calculated under
conditions that a signal 301 having the greatest amplitude is
considered as a mainpath signal and the remaining signals 302 and
303 are considered as multipath signals and noises.
In step 202, using the SMNRs calculated in step 201, two or three
beams having a large SMNR are primarily selected. The number of the
primarily selected beams is determined by the number of beams that
are applied to the DTV receiver. Here, the selected beams have the
possibility that can improve the performance of the DTV
receiver.
In step 203, SDMRs with respect to the primarily selected beam
output signals are calculated using the corresponding channel
impulse responses. That is, the SDMRs are calculated by the ratio
of the mainpath signal to the multipath signal having the greatest
amplitude. The comparison under this condition can be a process of
checking the amplitude distribution of the multipath signals. When
the SMNRs of the primarily selected beam output signals are similar
to one another, if a beam output signal having one large multipath
signal and beam output signals having several small multipath
signals exist, the selection of the latter is excellent to the
equalizer side in terms of the performance improvement. Step 204 is
a process that considers this fact.
In step 204, the SDMRs are compared in the channel impulse
responses of the two or three beam output signals selected
primarily, and the beam output signal (output signal of the
demodulator) having the greatest SDMR is finally selected.
FIGS. 3 to 7 illustrate channel impulse responses of the beam
outputs according to beam steering angles used in the beam
selecting method of FIG. 2.
FIG. 3 illustrates a channel impulse response of a first beam
output when a beam steering angle is -30.degree., FIG. 4
illustrates a channel impulse response of a second beam output when
a beam steering angle is -15.degree., FIG. 5 illustrates a channel
impulse response of a third beam output when a beam steering angle
is 0.degree., FIG. 6 illustrates a channel impulse response of a
fourth beam output when a beam steering angle is 15.degree., and
FIG. 7 illustrates a channel impulse response of a fifth beam
output when a beam steering angle is 30.degree..
In using the selection type method, channel impulse responses as
illustrated in FIGS. 3 to 7 are primarily selected, and a channel
impulse response as illustrated in FIG. 3 is finally selected
according to application of a secondary selection condition.
FIG. 8 is a flowchart of a beam combining method for improving a
digital broadcasting reception performance in accordance with an
embodiment of the present invention. The beam combining method is
carried out in the beam combiner 105.
In step 401, the beam combiner 105 calculates SMNRs with respect to
the respective beam output signals using channel impulse responses
estimated by the correlator 104.
In step 402, using the SMNRs calculated in step 401, two beam
output signals having a large SMNR are primarily selected. If an
incident angle of a mainpath signal inputted to the antenna is
10.degree. and incident angles of the remaining multipath signals
are respectively -33.degree., -66.degree., 60.degree., 35.degree.
and 63.degree., channel impulse responses of five beam outputs are
exhibited like FIGS. 9 and 13. FIG. 12 illustrates the channel
impulse response having the greatest SMNR. From the five beam
outputs under the above conditions of the incident angles, it can
be seen that the cases of FIGS. 11 and 13 have small amplitudes of
the multipath signals with respect to the mainpath signal.
Therefore, if two beam output signals having a large SMNR are
selected, the channel impulse responses of FIGS. 11 and 13 are
sequentially selected. Using these results, a more excellent
channel improvement effect can be obtained.
In step 403, a delay time between mainpath signals of the two beam
output signals selected in step 401 are calculated. In step 404,
two beam output signals are combined using the calculated delay
time. When beam output results as illustrated in FIGS. 11 and 12
are added, a following process is required. Since two beams have
different directions, signals that become mainpath signals in the
respective beams have different time delays. Therefore, when adding
two output signals, it is necessary to compensate for time
difference of the mainpath signals. An equal gain combining (EGC)
method or maximal ratio combining (MRC) method is used as the
combining method.
FIGS. 9 to 13 illustrate channel impulse responses of the beam
outputs used in the beam combination of FIG. 8, showing channel
impulse responses of five beam outputs when the incident angel of
the mainpath signal inputted to the antenna is 10.degree. and the
incident angles of the remaining multipath signals are respectively
-33.degree., -66.degree., -60.degree., 35.degree. and
63.degree..
FIGS. 14 and 15 illustrates output signals of the equalizer in the
beam selection type DTV receiving apparatus and the beam
combination type DTV receiving apparatus, respectively. FIGS. 16
and 17 illustrates mean square error of the output signals of the
equalizer in the beam selection type DTV receiving apparatus and
the beam combination type DTV receiving apparatus, respectively.
FIGS. 18 and 19 illustrate tap coefficients of the equalizer in the
beam selection type DTV receiving apparatus and the beam
combination type DTV receiving apparatus.
TABLE-US-00001 TABLE 1 InputSNR Channel 10 11 12 13 14 15 16 17 18
Beam Osnr 11.48 12.10 12.72 13.31 14.03 14.46 16.42 19.90 21.52
Selection SER 0.39 0.36 0.32 0.29 0.25 0.23 0.13 0.03 0.01 Beam
Osnr 11.63 12.33 12.74 13.41 14.15 15.72 17.94 19.93 21.45
Combination SER 0.38 0.34 0.32 0.29 0.24 0.16 0.08 0.03 0.01
When comparing the performances of the beam selection type method
and the beam combination type method under the above conditions,
the results are given like FIGS. 14 to 19 and Table 1. Here, SER
represents a symbol error rate and Oser represents an output
SNR.
FIG. 14 illustrates an output signal of the equalizer when the beam
selection type DTV receiving apparatus is used in Brazil D channel.
A convergence speed and SNR state can be seen from FIG. 14. FIG. 15
illustrates an output signal of the equalizer when the beam
combination type DTV receiving apparatus is used. It can be seen
from FIGS. 14 and 15 that the beam combination type structure has a
faster convergence speed than that of the beam selection type
structure. Also, it can be seen from FIGS. 16 and 17 that the beam
combination type structure has a higher output signal to noise
ratio (SNR) after convergence than that of the beam selection type
structure.
FIGS. 18 and 19 illustrate tap coefficients after convergence of
the equalizer. In the equalizer tap coefficient of the receiving
apparatus using the beam combination type structure, tap
coefficient corresponding to position of the mainpath signal is
reduced to less than 1. This reason is that the mainpath signal
increases and the multipath signal decreases relatively due to the
addition of the selected beam output signal. Therefore, the
convergence speed of the equalizer becomes fast and the SNR of the
output signal increases.
Table 1 shows the comparison analysis of performance when the beam
selection type structure and the beam combination type structure
are used. When the input SNR ranges from 10 dB to 18 dB, the beam
combination type receiving apparatus has a high output SNR and a
low SER.
However, the use of the beam combination type structure does not
always help the performance improvement of the DTV receiving
apparatus. Because the amplitude of the mainpath signal increases
and the amplitude of the multipath signal decreases relatively when
two beam output signals are added, the beam combination type
structure can obtain more excellent performance than the beam
selection type structure. That is, only when the mainpath signal to
multipath signals ratios is increased or equal, the use of the beam
combination type structure can improve the performance of the
receiving apparatus. Therefore, the selection algorithm for
determining which one of the beam selection type structure and the
beam combination type structure will be used is important to
improve the reception performance. Whichever structure is selected,
the SMNR condition is used.
FIG. 20 is a flowchart of a hybrid beam selecting method for
improving the digital broadcasting reception performance in
accordance with an embodiment of the present invention. The hybrid
beam selecting method is carried out in the hybrid beam selector
105.
The present invention relates to a beam combining structure,
capable of improving DTV reception performance, and a hybrid beam
selecting method that selects one beam or combines more than two
beam output signals depending on the conditions.
Referring to FIG. 20, in step 901, the hybrid beam selector 105
calculates SMNRs with respect to the respective beam output signals
using channel impulse responses estimated by the correlator 104. In
step 902, two beam output signals having a large SMNR are primarily
selected using the SMNRs calculated in step 901. Specifically, as
illustrated in FIGS. 9 to 13, the SMNRs are calculated under
conditions that a signal having the greatest amplitude is
considered as a mainpath signal and the remaining signals are
considered as multipath signals and noises.
In step 903, a delay time (time difference) between mainpath
signals of the two beam output signals selected in step 902 is
calculated. In step 904, two beam output signals are combined
adjusting the calculated delay time (that is, the time difference
of the selected beam outputs is compensated and two signals are
added).
In step 905, the SMNR is calculated using the channel impulse
response of the combined beam output signals in step 904. In step
906, the calculated SMNR of step 905 is compared with the largest
value among the SMNRs of the primarily selected beams of step 902.
In step 907, it is determined whether the SMNR of the combined beam
output signal is greater than or equal to the maximal SMNR of the
selected beam output signal.
In step 908, when the maximal SMNR of the selected beam output
signal is greater than the SMNR of the combined beam output signal,
the beam is finally selected using the beam selecting method (see
FIG. 2). The beam selecting method has been described above with
reference to FIG. 2.
In step 909, when the SMNR of the combined beam output signal is
greater than or equal to the maximal SMNR of the selected beam
output signal, the beam combining method (FIG. 8) is used. That is,
the combined signal obtained in step 904 is outputted to the
equalizer.
The above-described methods in accordance with the present
invention can be stored in computer-readable recording media. The
computer-readable recording media may include CDROM, RAM, ROM,
floppy disk, hard disk, optical magnetic disk, and so on. Since
these procedures can be easily carried out by those skilled in the
art, a detailed description thereof will be omitted.
While the present invention has been described with respect to
certain preferred embodiments, it will be apparent to those skilled
in the art that various changes and modifications may be made
without departing from the scope of the invention as defined in the
following claims.
* * * * *